[REF] move event_bus into utils, readd 2 functions

tests/utils.test.ts

@@ -0,0 +1,35 @@
+import { EventBus } from "../src/utils";
+
+describe("event bus behaviour", () => {
+  test("can subscribe and be notified", () => {
+    const bus = new EventBus();
+    let notified = false;
+    bus.addEventListener("event", () => {
+      notified = true;
+    });
+    expect(notified).toBe(false);
+    bus.trigger("event");
+    expect(notified).toBe(true);
+  });
+
+  test("can unsubscribe", () => {
+    const bus = new EventBus();
+    let n = 0;
+    let cb = () => n++;
+    bus.addEventListener("event", cb);
+    expect(n).toBe(0);
+    bus.trigger("event");
+    expect(n).toBe(1);
+    bus.removeEventListener("event", cb);
+    expect(n).toBe(1);
+    bus.trigger("event");
+    expect(n).toBe(1);
+  });
+
+  test("arguments are properly propagated", () => {
+    expect.assertions(1);
+    const bus = new EventBus();
+    bus.addEventListener("event", (ev: any) => expect(ev.detail).toBe("hello world"));
+    bus.trigger("event", "hello world");
+  });
+});